A pioneering new drug appears to have cured a British man with advanced skin cancer who had been given just months to live.
Doctors cannot be certain it was the treatment that led to the "miraculous" outcome for 64-year-old Warwick Steele, but know of no other explanation.
Results from an early-stage trial of the drug indicate that it may offer a potential "paradigm shift" in cancer therapy, according to Steele's consultant.
The drug, pembrolizumab, is the latest in a new generation of treatments that prevent cancers shielding themselves from the immune system.
It was tested on melanoma - the most dangerous form of skin cancer - because the prospects for patients with advanced forms of this disease are so bleak.
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Just under 70 per cent of the 411 patients taking part in the trial were still alive one year after starting on the treatment.
The result is considered remarkable because all had highly advanced melanoma and a very poor prognosis.
Currently one-year survival rates for untreated patients diagnosed with advanced stage four melanoma are just 10 per cent for men and 35 per cent for women.
Steele, a television engineer from Ruislip, west London, had undergone six months of treatment with pembrolizumab, which is injected into the bloodstream.
Doctors were astonished when after just three months his tumours had almost disappeared. Since then they have shown no sign of returning - and in fact have shrunk even further.
"We cannot say for certain that he's been cured, but he is doing very well," said his consultant, Dr David Chao, from the Royal Free Hampstead NHS Trust in London.
"He was aware that without an effective treatment his survival prospects were not good - maybe months.
"Pembrolizumab looks like it has potential to be a paradigm shift for cancer therapy and is firmly helping to establish immunotherapy as one of the most exciting and promising treatment modalities in recent years.
Pembrolizumab is a synthetic antibody that blocks a biological pathway called programmed cell death 1 (PD-1) which cancers activate to suppress the immune system.
In healthy individuals, PD-1 is part of the process that applies a "brake" to the immune system and prevents it running out of control.
Results from the trial were presented at the annual meeting of the American Society of Clinical Oncology in Chicago.
Pembrolizumab's manufacturer, the pharmaceutical company Merck Sharp & Dohme, is expected to apply for a European licence to market the drug within months.
